1. Field of the Invention
This invention relates to a treatment process for aluminum in a vacuum apparatus. More particularly, this invention relates to a process for treating exposed aluminum surfaces in a vacuum apparatus used for deposition and/or etching of materials on a semiconductor wafer.
2 Description of the Related Art
Aluminum and aluminum base alloys have been widely used as chamber materials in vacuum apparatus used for deposition and/or etching processes employed in the formation of integrated circuit structures on semiconductor wafers. Aluminum is a preferred vacuum chamber material both because of its relatively low cost and its non-reactivity with at least some of the chemicals used in such processes. For example, in CVD tungsten deposition, using WF.sub.6 gas, aluminum has been used to form the heated susceptor because of its excellent heat conductivity and resistance to fluorine, even at temperatures as high as 525.degree. C.
However, in certain processes, particularly CVD or PVD deposition processes, the inner surfaces of the vacuum chamber, including the aluminum surfaces within the chamber, become coated with materials which must be removed before further processing can be carried out in the chamber. The chemicals used in such cleaning steps, however, have been found to apparently also remove protective surfaces from the aluminum. This can result in vaporization or sublimation of aluminum from the cleaned aluminum surfaces when such surfaces are then exposed to temperatures above about 400.degree. C. during subsequent processing. Such vaporization or sublimation, in turn, results in undesirable aluminum depositions and/or particle formation in the vacuum chamber during such subsequent processing.
For example, in tungsten CVD deposition, tungsten metal may deposit on the exposed surface of the heated susceptor. NF.sub.3 or SF.sub.6 plasmas have been used to remove such tungsten deposits, but this, in turn, results in deposition of residuals, such as fluorine residues. In the related application of one of us, Chang U.S. Ser. No. 07/398,689, filed Aug. 25, 1989, abandoned, assigned to the assignee of this invention, and cross-reference to which is hereby made, it was proposed to remove such fluorine residues by flowing a gaseous source of hydrogen into the chamber and igniting a plasma.
While this process successfully removed the fluorine residues, it has been discovered that in vacuum chambers cleaned in such a manner, subsequent processing, e.g., deposition or etching processes, wherein the "cleaned" aluminum surfaces were exposed to temperatures in excess of about 400.degree. C., apparently resulted in vaporization and/or sublimation of aluminum. This, in turn, resulted in undesirable aluminum particle formation and/or depositions of the aluminum or aluminum alloy on other surfaces in the vacuum chamber, such as the chamber walls.
It would, therefore, be advantageous to be able to remove undesirable residues in a vacuum chamber having aluminum surfaces therein without rendering such aluminum surfaces more susceptible to such undesirable vaporization or sublimation.